The newest rookies arrived at Chargers Park this spring in all their infant glory. They met veteran teammates, eyes wide with respect.

His own stared back at him.

"I was like, 'Holy smokes. They look young,' " Mathews said. "I'm the old guy now. It's weird. Time flies. It seems like just last year that I was a rookie, having the 'whoa' factor of being next to Philip (Rivers) and (Antonio) Gates."

Time has been good for Mathews. He hopped aboard the NFL in 2010, expecting a pony when he got a bull that bucked and bounced around. The Chargers running back has a handle now in his fifth season. He looks to finish what he started in 2013 during what will be the final year of his rookie contract.

The NFL is said to be where a college kid becomes a man.

Mathews agrees.

"You come in as a rookie out of college; you don't know what to expect," Mathews, 26, said. "You think it's going to be easy. You were ballin' out in college. Now, in the NFL, you're playing against grown men, grown men that are fighting every day, that have families to feed, that come from all different backgrounds trying to be better than you and take your job.

"You learn real quick that nothing is given to you. Everything, you have to earn. It's just something you learn as you go along. The more years under your belt, the more knowledge you have."

A key part of his was physical.

Mathews had to learn the best method to prepare his body, both in workout regimen and diet.

His first offseason came during the lockout and lacked structure. The next year, he overcompensated. He trained, by all accounts, like a mad man at Chargers Park, bulking up only to break a collarbone on his first exhibition carry. He broke his other collarbone to end the regular season, and it was back to the drawing board.

He leaned up last year and rushed for a career-high 1,255 yards behind an improved offensive line.

Mathews weighed 227 pounds at minicamp last month, 9 pounds lighter than the same period in 2013. He is comfortable playing around 223 and 225 pounds during the season, so he is right on track.

"You come to realize your body is your weapon," Mathews said. "You got to take care of it. You need it working on all cylinders to play this game. ... You don't have to eat perfect. You have to eat smart. When I work out, my metabolism kicks up. I can't eat heavy things. If I do that, I'll be 240 by the time I'll get back to camp."

Last year was Mathews' banner season.

In his mind, it went unfinished.

Yes, he served as the workhorse during a closing run to the playoffs. His 121 December carries, 58 of which came in a five-day span, led the league. And he played all 16 regular-season games, a number that looks nice on the stat sheet.

But ankle woes limited him down the stretch. Despite his best effort, he was forced to exit a playoff loss to the Broncos after five offensive snaps.

This offseason, Mathews' goal has been to go further.

More comfortable in the league, he knows what his body needs. "Little tweaks" in preparation, he said, can be the difference. He has spent time training in Los Angeles in advance to the July 24 start of training camp.

"I didn't get to contribute to ... the real games when they count," Mathews said. "That's what my expectation is this year. I've got to do more so I can be there with my guys to help them out as much as I can when we get into that position again."